| 摘要 |
PURPOSE:To prevent formation of coarse crystal grains and to obtain low carbon boron steel parts having excellent toughness surely by cold working a blank material of low carbon boron steel material of specific compsns. at limited working rates and subjecting the same to hardening and tempering. CONSTITUTION:The steel consisting of 0.15-0.30wt% C, 0.15-0.35% Si, 0.60- 1.60% Mn, <=1.20% Cr, 0.0005-0.0030% B, 0.01-0.04% Ti, 0.01-0.04% Al, and the balance Fe and unavoidable impurities is used as a blank material. Such blank material is beforehand formed to a size larger than the shape of products and is subjected to cold working such as cold forging at >=13% working rates. Thereafter, the material is applied with hardening and tempering treatments. By such method, the formation of coarse crystal grains is prevented, and the fine grains of which the grain sizes of the old austenite crystal after the hardening is >=5 ASTM grain size number are obtained surely. This method is used for production of parts for structural purposes such as bolts. |
